Coping with climate change. Energetic costs of avian timing of reproduction

PhD ceremony: Mr. L. te Marvelde, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Coping with climate change. Energetic costs of avian timing of reproduction

Promotor(s): prof. M.E. Visser

Faculty: Mathematics and Natural Sciences

The breeding success of most forest birds, like great tits, strongly depends on the timing of breeding relative to the timing of the caterpillar food peak. Climate change caused the annual food peak to advance. Luc te Marvelde studied why great tits advanced breeding, but not sufficiently to match the shift of the food peak.

One possible explanation for the lack of shift is that there is not enough food to start laying early enough to be synchronized with the caterpillar food peak. Te Marvelde monitored insect availability and great tit foraging behaviour simultaneously and reported that females foraged in those trees which at that moment had highest insect availability, even though seeds, which contain much more energy, were abundant. Laying dates of the earliest laying great tits coincided with a steep increase in insect availability after a period of low insect abundance, suggesting a possible protein restriction on egg production.

Advancing laying to increase the synchrony between nestling food demand and caterpillar availability will come with an increased energetic costs during egg laying, as eggs will be produced under colder conditions while food availability and foraging efficiency are low. The fitness cost of the increasing energetic costs needed to advance egg laying may not outweigh the fitness benefits gained by breeding earlier and thus mismatched reproduction can be adaptive. Unfortunately Te Marvelde was not able to test if the current (mismatched) timing of reproduction is adaptive as he was not able to experimentally advance egg laying in free living great tits, which is needed to confirm this hypothesis.